Sorry, its a stupid paintball reference. It probably is meaningless. What its supposed to mean is that as a chemical pressurized (to the point of liquification) boils and creates the pressure in the tank, this pressure remains relatively stable as long as there is some liquid left to boil.
So most paintball markers use CO2 because you need a simple regulator to get an even pressure for most of the tank. Some markers use plain air pressure, they require more complicated regulators because the pressure changes dramatically during the entire use of the tank.
So the dumb jocks say that the CO2 tanks are "pressure stable", I suppose because pressure in the tank is constant around 850psi so long as there is any liquid CO2 in the tank.[1]
I made this comment because this to me seems like a desirable property for a fuel gas in a compressed gas vehicle to possess. I will attempt to be more succinct in the future.
[1] And since we are nitpicking, I am in fact aware that that this figure of 850 is variable based on the temperature of the tank.
The only trouble with using a gas like co2 that liquefies easily is that once you reach that point (850psi) you pretty much can't go any farther. And they are running this thing at a much higher pressure than that - about 4500.
I'm sure there are gases that would liquefy at this pressure, but none that you would want to release into the atmosphere.
